The present invention relates to methods for treating a subterranean environment. More particularly, the present invention relates to the remedial treatment of a subterranean environment with pressure pulsing and consolidating agents.
Gravel packing operations are commonly performed in subterranean formations to control unconsolidated particulates. A typical gravel packing operation involves placing a filtration bed containing gravel particulates near the well bore that neighbors the zone of interest. The filtration bed acts as a sort of physical barrier to the transport of unconsolidated particulates to the well bore that could be produced with the produced fluids. One common type of gravel packing operation involves placing a sand control screen in the well bore and packing the annulus between the screen and the well bore with gravel particulates of a specific size designed to prevent the passage of formation sand. The sand control screen is generally a filter assembly used to retain the gravel placed during the gravel pack operation. In addition to the use of sand control screens, gravel packing operations may involve the use of a wide variety of sand control equipment, including liners (e.g., slotted liners, perforated liners, etc.), combinations of liners and screens, and other suitable apparatus. A wide range of sizes and screen configurations are available to suit the characteristics of the gravel particulates used. Similarly, a wide range of sizes of gravel particulates are available to suit the characteristics of the unconsolidated particulates. The resulting structure presents a barrier to migrating sand from the formation while still permitting fluid flow.
One problem encountered after a gravel packing operation is migrating fines that plug the gravel pack and sand control screen, impeding fluid flow and causing production levels to drop. As used in this disclosure, the term “fines” refers to loose particles, such as formation fines, formation sand, clay particulates, coal fines, resin particulates, crushed proppant or gravel particulates, and the like. These migrating fines can also obstruct fluid pathways in the gravel pack lining the well. In particular, in situ fines mobilized during production, or injection, can lodge themselves in sand control screens and gravel packs, preventing or reducing fluid flow there through. Similar problems are also encountered due to scale buildup on sand control screens and gravel packs, as well as precipitates (e.g., solid salts (e.g., inorganic salts such as calcium or barium sulfates, calcium carbonate, calcium/barium scales)) on the sand control screen and the gravel pack.
Well-stimulation techniques, such as matrix acidizing, have been developed to remediate wells affected by these problems. In matrix acidizing, thousands of gallons of acid are injected into the well to dissolve away precipitates, fines, or scale on the inside of tubulars, trapped in the openings of the screen, in the pore spaces of gravel pack or matrix formation. A corrosion inhibitor generally is used to prevent tubulars from corrosion. Also, the acid must be removed from the well. Often, the well must also be flushed with pre- and post-acid solutions. Aside from the difficulties of determining the proper chemical composition for these fluids and pumping them down the well, the environmental costs of matrix acidizing can render the process undesirable. Additionally, matrix acidizing treatments generally only provide a temporary solution to these problems. Screens, preslotted liners, and gravel packs may also be flushed with a brine solution to remove solid particles. While this brine treatment is cheap and relatively easy to complete, it offers only a temporary and localized respite from the plugging fines. Moreover, frequent flushing can damage the formation and further decrease production.
Pressure pulsing is another technique that has been used to address these problems. “Pressure pulsing,” as used in this disclosure, refers to the application of period increases, or “pulses,” in the pressure of fluid introduced into the formation so as to deliberately vary fluid pressure applied to the formation. Pressure pulsing has been found to be effective at cleaning fluid flow lines and well bores. The step of applying the pressure pulse to the fluid may be performed at the surface or in the well bore. Pulsing may occur using any suitable methodology, including raising and lowering a string of tubing located within the well bore, or by employing devices, such as a fluidic oscillators, that rely on fluid oscillation effects to create pressure pulsing. In some embodiments, the pressure pulse may be generated by flowing the fluid through a pulsonic device, such as a fluidic oscillator. For instance, the fluid may be flowed through a suitable pulsonic device that is attached at the end of coiled tubing so as to generate the desired pressure pulsing in the fluid. Generally, the fluid may be flowed into the pulsonic device at a constant rate and pressure such that a pressure pulse is applied to the fluid as it passes through the pulsonic device.